This invention relates to a multilevel modulator which has an error correcting code producing unit and to a multilevel demodulator for use as a counterpart of the modulator.
For the multilevel modulator of the type described, it is desirable that a modulating signal have an increased number of levels. This is because the increased number of levels makes it possible to effectively utilize a carrier level. Therefore, a large-capacity digital radio communication network ordinarily comprises the multilevel modulator. In such a digital radio communication network, a transmission error, namely, a code error, of transmission information is reduced by an error correcting system which makes use of an error correcting code. As the error correcting code, a Lee-error correcting code is well known in the art. The error correcting system is exemplified in an article contributed by Katsuhiro Nakamura of NEC Corporation, namely, the present assignee, to ICC Conference Record, Vol. 4-3 (June 1979), pages 45.4.1 to 45.4.5, under the title of "A Class of Error Correcting Codes for DPSK Channels."
With an increase in the modulating signal levels, the error correcting code requires an increased number of bits. Accordingly, the error correcting code producing unit must carry out a large amount of logical operation on producing the error correcting code. As a result, the error correcting code producing unit becomes bulky and expensive. This applies to the multilevel demodulator.